（急）为什么有的session只有一个TX lock而没有TM lock？

foxmile

了解一下。

lilyzhang918

原帖由 Yong Huang 于 2007-12-15 11:57 发表


Sometimes the SQLs you get from v$session.sql_hash_value or prev_hash_value are still not previous enough. The session could have done some distributed transactions earlier creating TM locks on the remote side and only TX locks locally.

Yong Huang

You are right. I can reproduce this problem by following steps:
1. Run a SQL in session A to query remote database.
2. Check V$LOCK, session A will hold a TX lock.
3. Run a SQL in session A to query local data.
4. Check V$LOCK, session A still hold the TX lock.

我本来以为如果做过distribute transaction都应该有一个DX的lock，即使是只做了query。所以之前没看到DX的lock就没往那里想。结果今天发现9i才会有DX的lock, 8i是没有的。

谢谢Yong Huang和大家的帮助。

Yong Huang

原帖由 lilyzhang918 于 2007-12-20 03:12 发表
...
我本来以为如果做过distribute transaction都应该有一个DX的lock，即使是只做了query。所以之前没看到DX的lock就没往那里想。结果今天发现9i才会有DX的lock, 8i是没有的。

谢谢Yong Huang和大家的帮助。

Actually, DX locks are in Oracle 7 and all later versions. The weird thing is that sometimes it does not show up in a session that does not create it. I mean, if you have a distributed transaction (including a query), the DX may not show up in a different session that monitors the first session. I think it only shows up if the first session's status is active (v$session.status='ACTIVE'). But in the first session itself, it should show.

Another weird thing is that if the database link is to the localhost (not to another DB server), DX locks won't show up.

Yong Huang

foxmile

意思是，在select 的时候也会有tx锁？